Marine riser support system



March 24, 1970 W H. PETERSEN MARINE RISER SUPPORT SYSTEM Filed May 29, 1968 3 Sheets-Sheet 1 INVENTORI BYI WILLIAM H PETERSEN HIS ATTORNEY W. H. PETERSEN MARINE RISER" SUPPORT SYSTEM March 24, 1970 3 Sheets-Sheet 2 Filed May 29, 1968 FIG.

N F- s OY T E E N P m T H T A M R m w L, m w m B 3 March 24, 1970 w. H. PETERSEN MARINE RISER SUPPORT SYSTEM 3 Sheets-Sheet 5 Filed May 29, 1968 INVENTORI WILLIAM H. PETERSEN BY:

HIS ATTORNEY United States Patent U.S. Cl. 166.5 9 Claims ABSTRACT OF THE DISCLOSURE Method and apparatus for connecting a marine conductor pipe assembly depending from a floating vessel to an underwater wellhead structure by pulling said assembly downwardly into engagement with the structure against an upwardly directed, substantially constant force being applied to the assembly.

This invention relates to a method and apparatus for use in drilling, completing and working-over operations in oil and gas wells at offshore locations. More particularly, the subject invention pertains to a method and apparatus for effecting communication between a vessel on the surface of a body of water and a wellhead structure positioned on the sea bed or at a substantial depth below the surface of the water.

In an attemptto locate new oil fields, an increasing amount of well drilling has been conducted at offshore locations, such for example, as off the coasts of California, Louisiana and Texas. As a general rule, the strings of casing in a well, together with the tubing strings or string, extend to a point above the surface of the water where they are closed in the conventional manner that is used with respect to onshore wells, with a conventional wellhead assembly being attached to the top of the easing. Such arrangements constitute a hazard to navigation, and recently methods and apparatus have been developed for drilling and completing wells wherein both the well casinghead, and subsequently the wellhead assembly and easing closure device, are located underwater at depths suflicient to allow ships to pass over them, Underwater structures of this type are, of course, exposed to conditions such as the corrosive nature of the sea water and the presence of marine life which tends to grow and become encrusted on metallic structures below the surface of the water.

Since it is necessary from time to time to go back into a well wherever it has been completed for servicing or workover operations, it is desirable to have an underwater wellhead structure of suitable design so that communication may be had with the interior of the well itself or, alternatively, so that at least a portion of the structure may be removed to the surface of the water for maintenance operations. An underwater arrangement of this sort is shown and described in US. Patent No. 3,064,735, issued Nov. 20, 1962, to R. J. Bauer et a1.

Since the depths at which such underwater structures are often placed are of such magnitude as to preclude use of divers, a number of approaches have been devised for remotely establishing communication between these underwater structures and vessels floating on the surface of a body of water so that the desired workover operations may be carried out. One technique that has found considerable acceptance is that of lowering a wellhead connector by means of a pipe string or marine conductor pipe from the vessel into locking engagement with the underwater wellhead assembly. Tubing members may be disposed within the marine conductor pipe to cooperate with similar members within the assembly and/or'well casing so that the various operations may be carried out. Copending US. application Ser. No. 731,381, filed May 23, 1968, discloses one suitable marine conductor pipewellhead connector arrangement that may be utilized when carrying out operations of the above-described nature.

One of the problems encountered when remotely attaching a wellhead connector to an underwater structure is that not only must such operation be carried out from a vessel several hundreds of feet above but, in addition, the up and down movement of the floating vessel and marine conductor pipe depending therefrom makes it difficult to control the positioning of the pipe and connector with respect to the fixed wellhead structure. For example, a sudden drop of the floating vessel due to wave or other surface activity of the water during the connecting operation may result in buckling of the marine conductor pipe or damage to the underwater structure or connector.

SUMMARY OF THE INVENTION It is therefore a primary object of the present invention to provide a method and apparatus whereby a controlled remote connection may be made between an underwater wellhead structure and a marine conductor assembly, including a connector and a marine conductor pipe, depending from a floating vessel, regardless of the degree of up and down motion of the vessel.

A further object of this invention is to provide a method and apparatus whereby a controlled pull down of a marine conductor assembly, including a connector and a marine conductor pipe, onto an underwater wellhead structure may be eflected from a floating vessel from which the marine conductor assembly depends, with the distance between said marine conductor assembly and said structure remaining substantially constant during a given stage of the pull down operation regardless of the degree of up and down movement of the floating vessel.

These objects have been attained in the present invention by providing apparatus for remotely connecting marine conductor assembly means extending from a floating vessel to an underwater assembly means wherein yieldable support means is provided on the vessel to urge the marine conductor assembly means in a substantially upward direction with a force greater than the weight of the marine conductor assembly means, An arrangement including sheave means is associated with the vessel to function as a motion cancellation mechanism with respect to up and down movement of the vessel and also upon actuation of a pull-down line associated therewith to serve to bring the marine conductor assembly means into operative engagement with the underwater assembly means against the upwardly directed force exerted by the yieldable support means.

DESCRIPTION OF THE DRAWING These and other objects of this invention will be understood from the following description taken with reference to the drawings wherein:

FIGURE 1 is a diagrammatic view taken in longitudinal projection illustrating the lower portion of a floating vessel having depending therefrom a marine conductor assembly prior to its operative engagement with an underwater wellhead structure;

FIGURE 2 is a diagrammatic view taken in longitudinal projection and in enlarged detail of a portion of the floating vessel and the pulldown and motion compensatting apparatus according to the present invention;

FIGURE 3 is a side view in enlarged detail of a clamp and sheave member utilized in the arrangement of FIG- URE 2; and

FIGURES 4 and 5 are schematic illustrations showing the operation of the motion compensating apparatus according to the present invention during the rise and fall of the floating vessel.

Referring to FIGURE 1 of the drawing, a platform or barge 11 of any suitable floatable type is illustrated as floating on the surface of a body of water 12 and positioned over a preselected well site by suitable barge positioning means or by being anchored to the sea bed 13 by suitable anchors (not shown) connected to anchor lines 14 and 15. Equipment of this type may be used when carrying on well workover Operations in water depths varying from about 100 to 1,500 feet or more. The vessel is equipped with a conventional derrick 16 as well as other usual auxiliary equipment needed during workover operations relating to a well such as a rotary table '17, a hoist system (not shown), etc. The derrick 16 is preferably, but not necessarily, positioned on an elevated rig floor or operating platform 18 which is supported by means of a framework 19 over slot or well 20. When using the apparatus and method according to the present invention, the slot 20 may be either centrally located or extend in from one edge. However, operations may be carried out over the side of the barge or vessel without the use of a slot as from a portion of the operating platform extending out over one end of the remainder of the vessel.

An underwater wellhead structure, generally represented by numeral 21 in FIGURE 1, is illustrated as comprising a base member 22 which is positioned on the sea bed 13 and fixedly secured to conductor pipe or a large diameter well casing 23 which extends down into a well which has been previously drilled, and is preferably cemented therein. A pair of vertically-extending guide columns 24 and 25 are afiixed to base member 22 for the purpose which will be more fully brought out below. Disposed between guide columns 24 and 25 is a production wellhead assembly 26 which is of conventional design. Although illustrated herein in somewhat schematic fashion, it may be assumed that the disclosed assembly is of the general type disclosed in the above-mentioned U.S. Patent No. 3,064,735, issued Nov. 20, 1962, to R. J. Bauer et al. The assembly includes at least one production flow line 26a which is connected by suitable coupling means to underwater pipeline 26b. Assembly 26 is maintained in operative communication with well casing 23 by means of a conventional wellhead connector unit 27. An elongated landing mandrel or entry conduit 28 is fixedly secured at its lower end to the topmost portion of the remainder of assembly 26. Production wellhead assembly 26 differs from that disclosed in US. Patent No. 3,064,735 in that entry conduit or landing mandrel 28 has extending therefrom in an offset manner a bracket member 29 with a mono-post 30 atfixed thereto and extending vertically therefrom.

A single guide cable 31 is affixed to the end of monopost element 30 and extends upwardly to vessel 11. The guide cable 31 may be permanently atached to mono-post 30 or may be secured thereto by suitable latch means which has been previously remotely brought into engagement with the mono-post by means of suitable apparatus manipulated from vesel '11. One suitable apparatus for performing this is disclosed in copending U.S. application Ser. No. 749,171, filed July 31, 1968. In this last-mentioned application a specially designed tool incorporating wellhead assembly locating and positioning means, such as a TV camera and/ or a sonar unit, is lowered by means of a pipe string from a floating vessel onto the assembly to attach a latching element and cable or guide line to a mono-post. As previously stated, however, the cable may be permanently attached to the mono-post with grappling hooks or other means being employed to initially establish a connection between the free end of the cable and the vessel. As shown in FIGURES 1 and 2, the cable or monoguideline 31 passes over sheave 32, which is rotatably mounted on arm 33, and thence to a hoist 34 of any known design which is fixedly mounted on deck member 35 of vessel 11.

A marine riser or conductor pipe 36 with tubing members 36a and 36b disposed therein depends from vessel 11 and is biased in an upwardly direction under a substantially constant predetermined force by means of a hydraulic tensioner 37 of any known type. The tensioner is illustrated schematically in FIGURE 2 and essentially comprises a housing 38 having disposed therein a double acting hydraulic piston 39 which is afiixed in any desired fashion to the upper portion of marine conductor 36. A substantially constant upward presur is exerted on piston 39 and hence marine conductor 36 by pressuring up the lowermost end of housing 38 with hydraulic fluid through conduit 40. A conventional hydraulic accumulator arrangement (not shown) is in communication with conduit 41 near the upper portion of housing 38 to maintain the upwardly directed force at a substantially constant value. Although a hydraulic tensioer has been illustrated and described for providing the upwardly directed force, other expedients may be utilized to effect this end. For example, a counterweight system similar to that disclosed in US. Patent No. 3,221,817, issued Dec. 7, 1965, to De Vries et al. could be used for this purpose.

Disposed at the lower end of marine conductor 36 is a wellhead connector 42 (FIGURE 1) of any desired type and construction. The connector is of a size and having a bore to fit telescopically onto and to make sealing engagement with landing mandrel 28 of wellhead assembly 26. If desired, guideline connector means may be frame mounted on the connector 42 to establish guidelines 43 and 44 between the vessel 11 and the underwater wellhead structure 21. The guideline connector means forms no part of the present invention but is shown here for purposes of illustration only. Quite briefly, the form shown comprises cylindrical housing members 45 and 46 in which latch connector members 47 and 48, respectively, are freely disposed. Latch connector members 47 and 48 are held in the position illustrated in FIGURE 1 by virtue of the fact that guide cables 43 and 44 are maintained under tension by constant tension hoists 49 and 50 on vessel 11. The constant tension hoists 49 and 50 may be of any suitable design and exert a tensile force on the guide cables -to maintain the cone-shaped members 51 and 52, which constitute portions of latch connector members 47 and 48, against the respective bottoms of cylindrical housing members 45 and 46. It is to be understood that upon release of the force imparted by the constant tension hoists 49 and S0, latch connector membres 47 and 48 will be free to drop downwardly through the cylindrical housing members. The particular arrangement shown here is more fully disclosed in copending US. patent application Ser. No. 731,382, filed May 23, 1968. As stated above, however, the guideline or cable connecting means forms no part of the present invention.

As may also be seen with reference to FIGURE 1 a guide housing 53 defining a throughbore is frame mounted on the connector 42. The mono-guideline 31 passes through the throughbore of the guide housing to stabilize the connector and related apparatus as lowering operations are carried out from the vessel. These operations will be described in greater detail below.

With particular reference to FIGURES 1 and 2, a pulldown line or cable 54 is connected by attachment member 55 to a bracket 56 extending from an upper section of marine conductor pipe 36. The pull-down line 54 then passes under pulley or sheave 57 which is afiixed for rotatable movement on mono-guideline 31 at a predetermined location below bracket 56. Although any suitable means may be used to attach pulley 57 to mono-guideline 31, a hydraulic clamping mechanism is preferred since such an arrangement offers the advantage of permitting the operator to readily position the pulley 57 at any desired location on the mono-guideline and also providing a positive grip of great magnitude to be made with respect to the mono-guideline upon application of hydraulic pressure. FIGURES 2 and 3 illustrate one form of hydraulic clamping mechanism 58 which may be used for this purpose. Such apparatus is well known in the art so no attempt will be made here to discuss the operation thereof in great detail. Suffice it to say that the clamping mechanism comprises relatively movable clamping portions 59' and 60 which are brought into engagement over mono-guideline 31 through application of hydraulic pressure by hydraulic lines 61 and 62.

After passing under pulley 57, pull-down line 54 passes upwardly and over still another sheave or pulley 63 (FIG- URES 1 and 2) rotatably mounted on the free end of arm 33 and thence to a hoist or power .winch '64 mounted on deck member 35 of vessel 11. Arm 33 is integrally attached to a hydraulic piston member 65 which is disposed within cylinder 66 connected to operating platform 18 by any desired means. A hydraulic accumulator 67 is aflixed to cylinder 66 and communicates with the interior thereof in the known manner to bias piston member 65 in an upward direction so that a tensional force of a predetermined magnitude is applied to both mono-guideline 31 and pull-down line 54, which pass over pulley 32 and pulley 63, respectively.

FIGURES 4 and 5 illustrate in schematic fashion the mode of operation of the above-described apparatus. In FIGURE 4, an attempt has been made to show the relative positions assumed by the various elements of the invention when vessel -11, due to wave action or otherwise, is in its lowest position, i.e. when vessel 11 is at its closest position with respect to the underwater wellhead structure 21. FIGURE 5, on the other hand, shows vessel 11 at its extreme upward position, i.e. the position assumed thereby when it is at its maximum distance from structure 21. It should be noted that in both instances wellhead connector 42 is a substantially fixed distance, indicated by the letter X, from structure 21. This is due primarily to the fact that the previously described combination of piston member 65, cylinder 66 and accumulator 67 operates essentially as a pneumatic spring which permits arm 33 to either extend or retract. This arrangement keeps mono-guideline 31 taut at all times regardless of the up and down movement of vessel 11 with piston member 65 moving back and forth within cylinder 66 to accommodate for such vessel movement. Any given point, such as point A, :on mono-guideline 31 therefore, remains in substantially fixed relationship to ocean floor or sea bed 13. As previously described, both sheave 32 (over which mono-guideline 31 passes) and sheave 63 are ganged for rotatable movement on arm 33. For this reason, a given point, such as point B, lying on pull-down line 54 between sheave or pulley 63 and pulley 57 will remain at a substantially fixed relative position with respect to both point A on mono-guideline 31 and sea bed 13, regardless of the degree of up and down motion of vessel 11.

The pneumatic force being applied to piston member 65 being somewhat greater than that being applied to piston 39, the result is that the marine conductor pipe 36 remains relatively stationary with respect to ocean bed 13 while moving relative to vessel 11 in response to that vessels heaving motion. Connector 42 depending from the lower end of the marine conductor pipe thus remains a substantially fixed distance X from the underwater wellhead assembly 21 despite the heaving motion of vessel 11. To lower the connector 42 and marine conductor 36 onto the wellhead assembly, hoist 64 on board the vessel is actuated and pull-down line 54 is Wound thereon. Since the pulling power of hoist '64 is greater than the upwardly directed force being applied to the marine conductor by virtue of piston 39, the marine conductor and connector are pulled downwardly until initial engagement is made between guide housing 53 (FIGURE 1) and mono-post 30. Still further downward movement of the marine conductor pipe 36 will place connector 42 into engagement with landing mandrel 28 of the wellhead assembly. Preferably, suitable orienting means such as a pin and slot arrangement (not shown) will be provided on said mono-post 30 and said guide housing 53 to ensure proper alignment between connector 42 and landing mandrel '28 before engagement therebetween. Align- 6 ment means of this type may be seen with reference to copending US. application Ser. No. 749,171, filed July 31, 1968. Since such feature forms no part of the present invention, no attempt will be made to describe same in more detail in the present application.

After connector 42 has been connected to landing mandrel 28 by any known locking means, tension or guidelines 43 and 44 will be released and latch connector members 47 and 48 will be free to fall onto guide columns 24- and 25, respectively, to effect attachment between the guide columns and guidelines 43 and 44. As previously stated, however, such feature forms no part of the present invention, being described here for purposes of illustration only. For further disclosure of an arrangement of this type, reference may be had to copending US. application Ser. No. 731,382, filed May 23, 1968.

I claim as my invention: 1. Apparatus for remotely connecting marine conductor assembly means extending from a floating vessel on the surface of a body of water to a wellhead assembly secured to a casinghead above the earth below said body of water, said marine conductor assembly means including a marine conductor pipe and connector means, said apparatus comprising:

yieldable support means attached to the floating vessel,

said support means being secured to the upper portion of said marine conductor pipe to urge the marine conductor assembly means in a substantially upward direction with a force greater than the weight of the marine conductor assembly means; first sheave means; means for mounting said first sheave means at a substantially fixed distance from said wellhead assembly;

second sheave means mounted on said floating vessel;

pull-down line means having one end thereof attached to said marine conductor pipe and having the other end thereof in operative association with a first line take-up means mounted on said floating vessel; said pull-down line means being in cooperative engagement with said first sheave means and said second sheave means whereby actuation of said first line take-up means serves to pull down said marine conductor assembly means against the force of said yieldable support means to bring the connector means into engagement with said wellhead assembly.

2. The apparatus according to claim 1 wherein means is mounted on said floating vessel to maintain a substantially fixed distance between the connector means and said wellhead assembly regardless of the degree of up-anddown motion imparted to said floating vessel by wave action or other water surface activity.

3. The apparatus according to claim 1 wherein said means for mounting said first sheave means comprises a guideline means attached to said wellhead assembly and extending to said floating vessel and a means for clamping said first sheave means on said guideline means whereby the sheave means is mounted for rotatable movement at a fixed point with respect to the guideline means.

4. The apparatus according to claim 3 wherein third sheave means is mounted on said floating vessel, said guideline means being operatively engaged with said third sheave means and connected to said second line take-up means mounted on the floating vessel.

5. The apparatus according to claim 4 wherein said second sheave means and said third sheave means are both mounted for rotatable movement and uniform linear movement on reciprocal means, said reciprocal means being biased by biasing means to maintain a constant uniform tension on said pull-down line means and said guideline means.

6. The apparatus according to claim 5 wherein said yieldable support means and said biasing means each comprise hydraulic cylinder and piston arrangements.

7. The apparatus according to claim 1 wherein said pull-down line means is attached to said marine conductor pipe at a distance from said wellhead assembly greater than the substantially fixed distance therefrom maintained by said first sheave.

8. The apparatus according to claim 7 wherein said pull-down line means extends from said marine conductor pipe, passes under said first sheave means and over said second sheave means while maintaining engagement with both of said sheave means.

9. In a method for remotely connecting marine conductor assembly means extending from a floating vessel on the surface of a body of Water to a wellhead assembly secured to a casinghead above the earth below said body of water, said marine conductor assembly means including a marine conductor pipe and connector means, the steps Comprising:

(a) positioning said marine conductor assembly means over said wellhead assembly;

(b) yieldably urging said marine conductor assembly means in an upward direction by applying an upwardly directed force of predetermined magnitude thereto;

(c) maintaining a substantially fixed distance between said connector means and said wellhead assembly regardless of the degree of up and down movement of said vessel due to wave action or other water surface activity by moving said marine conductor assembly means relative to said vessel; and

(d) bringing said connector means into engagement with said wellhead assembly by applying a downwardly directed force of greater magnitude than said upwardly directed force to said marine conductor assembly means.

References Cited UNITED STATES PATENTS CHARLES E. OCONNELL, Primary Examiner R. E. FAVREAU, Assistant Examiner US. Cl. X.R. 1757 

